The present invention is generally related to a method for modulating the density of an electron beam as it is released from a cathode, and in particular relates to coupling a cathode to a nonlinear transmission line to modulate an electron beam emitted by the cathode.
In many electron beam-related applications, it is highly desirable or necessary to be able to modulate the density of an electron beam as it is released from the cathode. In grid-controlled microwave tubes, such as inductive output tubes and planar triodes, this is done by applying a dc voltage between the cathode and anode of a vacuum diode and then using a control grid with a time varying voltage bias a very short distance (as little as ˜0.1 mm) from the cathode. The control grid bias determines the amount of current that is released from the cathode. The highest frequency of these tubes is limited by the electron transit time in the cathode to grid region. The requirement for a cathode control grid increases expense and complexity as well as introducing additional failure methods (such as inadvertent shorting of the cathode to the grid due to contaminates or warping of the grid or cathode).
In many accelerators, a modulated electron beam is created using laser light pulses to eject electrons from a photocathode. The laser system and associated focusing optics add considerable cost and complexity to accelerator cathodes.
This invention provides a novel and efficient way to modulate the current density of an electron beam emitted from a cathode without the need for complicated control grids or laser-based photoemission techniques used in current microwave tubes and accelerators.